With the demand in recent years for water conservation, the problem has arisen that in tank-type toilets, the reduction in the amount of flush water used to flush toilets has caused a drop in the water level head of flush water held in flush water tanks, weakening the force of flush water discharged from flush water tanks.
A known response to this issue has been to provide a water conserving tank with which flush water can be stored inside the flush water tank for supplying flush water to a toilet so as to cut the amount of flush water used in a single toilet flush without reducing the water level head, as set forth in Patent Document 1 (Specification of Unexamined Utility Model Application H05-87070), for example. Provided at the bottom of the side surface of this water conserving tank are a water discharge port for discharging flush water from the water conserving tank into the flush water tank when the interior of the flush water tank becomes empty, and an intake port at the top end of the side surface of the water conserving tank for intaking flush water into the water conserving tank, so that water can be exchanged such that water in the conserving tank does not stagnate.